1. Field of the Invention
The present invention relates to a method for forming a multi-layer metallic wiring structure, which is preferably used in the manufacturing process for semiconductor devices.
2. Prior Art
Recent, large scale, integrated semiconductor circuit devices have been so greatly minimized that very severe requirements are applied on reliability of an inter-layer metallic connection--i.e. through hole--between metallic wiring layers. To increase the reliability of a fined through hole, metal is generally plugged into the through hole by the use of the high-temperature aluminum sputter method or the blanket W-CVD method.
Hereinafter, one example of a conventional blanket W-CVD method will be explained with reference to drawings.
FIGS. 18A to 18C illustrate a manufacturing process of a semiconductor device whose multi-layer metallic wiring structure is formed by the conventional blanket W-CVD method.
As illustrated FIG. 18A, a first oxide film layer 2 (usually, a BPSG film layer) is accumulated on a silicon substrate 1. Then, first metallic wiring 3 is formed on the first oxide film layer 2 by the use of photolithography and dry etching.
Subsequently, as illustrated in FIG. 18B, a second oxide film layer 4 is accumulated on the first oxide film layer 2 and the first metallic wiring 3. After the upper surface of the second oxide film layer 4 is flattened by the resist etchback method or the CMP (Chemical Mechanical Polishing) method, a through hole 5 is opened by photolithography and dry etching. Thereafter, a Ti-series sputter film layer 6 and a W-CVD film layer 7 are accumulated, and the W-CVD film layer 7 is flattened by the etchback method until the second oxide film layer 4 is bared entirely. In this case, the etchback method can be replaced by the CMP method and also both the second oxide film layer 4 and the W-CVD film layer 7 can be flattened simultaneously.
Next, as illustrated in FIG. 18C, a metallic film layer is accumulated on the second oxide film layer 4. Then, this metallic film layer is etched to form second metallic wiring 8, thereby accomplishing the formation of a two-layer metallic wiring structure.
Such a method of filling up the through hole 5 with metallic material for providing a conductive path between two metallic wiring brings merits of:
(1) increasing the reliability of a through hole remarkably; PA1 (2) forming the conductive path with better efficiency even if the through hole diameter is very small (i.e. a high aspect ratio through hole); and PA1 (3) flattening the metallic film above the through hole. PA1 (1) Since the mask information for a through hole is involved in either the mask pattern for the first-layer metallic wiring or the mask pattern for the second-layer metallic wiring, the number of photo masks required in the forming process of a two-layer metallic wiring structure can be reduced, for example, from three to two; PA1 (2) Etching process conventionally required for forming a through hole can be omitted; PA1 (3) As the fourth and fifth aspects of the present invention inherently provide plugging-type wiring, flatness of the second-layer metallic wiring is improved; PA1 (4) Possibility of mask deviation in the photolithography can be reduced, for example, from two to one; PA1 (5) As the through hole is filled with metal serving as a contact, reliability of the wiring can be improved at the region of this contact; and PA1 (6) Reliability of the contact is improved since the largeness of the through hole is kept constant.
However, above-described conventional method is disadvantageous in that at least three masks are required for formation of the two-layer metallic wiring structure comprising the first metallic wiring, the through hole and the second metallic wiring.
Furthermore, in the case where the blanket W-CVD plugging method is adopted, it will encounter with other problems, such that costs for film accumulations by sputtering, CVD deposition and etchback will increase the overall cost of the wiring process greatly.
Moreover, at least two alignments--one for the first metallic wiring and the through hole, and the other for the through hole and the second metallic wiring--are required in the photolithography. This will result in a problem that alignment deviation arises easily.